Generally, a gas sensor is classified into a semiconductor type, an oscillator type, a solid electrolyte type, an electrochemical type, a catalytic combustion type and so on according to an operation principle thereof. Among them, the semiconductor type gas sensor senses a certain chemical component using a change in a work function and an electric resistance occurring when a gas is in contact with a surface of a semiconductor. Among ceramic semiconductors, a semiconductor which has a high electrical conductivity and a high melting point and is thus thermally stable in a temperature range of use is used in the sensor. The semiconductor type gas sensor exhibits a response to a combustible gas, thus detects many kinds of gases, allows a sensor to be easily manufactured, makes a detection circuit configuration simple and exhibits stable thermal characteristics at room temperature.
The semiconductor type gas sensor has a package structure in which a gas sensing material or sensing chip is mounted on a substrate and needs a separate cap for protecting an upper surface of a sensing part or a sensing chip. A mesh formed of a fine net is installed on the cap so that an inside of the case can be ventilated to an outside through a plurality of holes.
However, since the above-described semiconductor type gas sensor uses a wire bonding method to connect a sensor chip with an electrode, a height of an upper structure thereof is increased, and thus a size of an entire package is increased a few times to a few tens times compared to a size of the sensor chip. Such a semiconductor type gas sensor has a disadvantage that it is still difficult to be applied to small electronic products or applications of information technology (IT).